In recent years, wristwatches of various types using a radio wave have been commercialized.
Specifically, there are known radio-equipped wristwatches formed such that radio functionality is added into a wristwatch to receive a broadcast radio wave and to acquire predetermined information, and radio controlled timepieces or remote controlled wristwatches in which a standard radio wave carrying time code is received to self-adjust the time of the wristwatch in use to the standard time.
However, for such a wristwatch to use a radio wave, it is necessary that a timepiece component configuration or design should be completely different from a timepiece component configuration or design of the conventional time pieces, and also consideration not to impair the reception performance is necessary.
More specifically, with the wristwatch, there exists a problem in which how to improve the reception performance of the antenna, in one aspect and further there exists design limitations regarding the size and design since the antenna is disposed in the wristwatch or in a portion of an outer casing, in other aspect.
In particular, the antenna greatly influencing the radio-wave reception performance has a relatively large size as compared with other components of a conventional wristwatch, and layout limitations are imposed in relation to the reception performance. As such, conventionally, antennas of various types such as an internally mounted type, an externally mounted type, an extendable type, and a code type are employed.
As the internally mounted type, a bar antenna formed of a magnetic core and winding is mainly used in the past.
In the case, however, when the antenna is mounted inside the wristwatch, engineering needs to be carried out for a case-body material, structure, design, or the like so as not to reduce the reception performance of the antenna.
In the case of the code type concurrently using, for example, the externally mounted type and the extendable type used with radio cassette units, earphones, and the like, engineering needs to be carried out providing considerations regarding the design of the overall timepiece and storability and durability thereof.
Under these circumstances, in order to further improve the wristwatch in terms of ornamental design in addition to further minimization and portability, considerations need to be provided, of course, not to introduce reduction in the reception performance of the antenna device and also to introduce the portability and ornamental design thereof.
Regarding the radio controlled timepiece, what determines the reception performance are antenna characteristics and reception circuit characteristics.
In a present stage, a lower limit of an input signal of a reception circuit or a reception IC is a signal amplitude of about 1 μV. To obtain practical reception performance, a reception antenna is required to have a capablity of obtaining an output having the signal amplitude of about 1 μV at an electrofield intensity (signal intensity) of 40 to 50 dB μV/m.
As such, with size limitations being imposed, it is a general practice to use a reception antenna of a resonance type allowing the signal output to be increased.
As the type of the reception antenna, since the wavelength of the radio wave is long, it is a general practice to use a bar antenna formed with a conductor wire wounded around a magnetic core.
In this kind of antenna, the output of the reception antenna thus formed is substantially proportional to the size of the reception antenna, so that a size of the antenna cannot be reduced to be so small to acquire practical reception performance. In the case of a small one such as a wristwatch, factors such as reception performance and layout are problems.
In addition, the output of the reception antenna is substantially reduced when the antenna is provided inside a metal outer case.
For this reason, for the wristwatch, to utilize radio waves, a component configuration and design being completely different from a component configuration and design of a conventional timepiece are required, and in addition, consideration not to impair the reception performance is also necessary.
For wristwatches, the compactness, thinness, portability, degree of design freedom, and massive feeling (high class feeling) are important factors, and a configuration in which an antenna is built-in inside a metal outer casing of a wristwatch is demanded.
Conventional radio controlled timepieces primarily use the technique in that the antenna is externally mounted on the timepiece or the technique in that the antenna is internally mounted inside the timepiece.
For a wristwatch with a bottom cover section and a side section each being made of a metal material, it is a general practice to mount the reception antenna on an external surface of the watch.
An outer casing of the reception antenna is formed by using non-metallic material such as a plastic material or the like so as not to reduce the reception performance, whereby it has a shape greatly protruding out of periphery of the watch. This impairs the compactness, thinness, and portability, and particularly reduces the degree of design freedom.
In the system in which the reception antenna is internally mounted inside he watch, the material such as a ceramic or plastic material for the outer casing (the bottom cover section and the side section) is used not to reduce the reception performance. However, since the strength of the material is low, the thickness of the timepiece becomes thick, thereby impairing the storability and portability, and increasing design limitations.
Further, the timepiece is formed with a low massive feeling in appearance.
As such, conventionally, as disclosed in Japanese Unexamined Patent publication Laid-open No. H2-126408, a metal antenna is disposed in a leather band of a wristwatch.
In addition, as disclosed in the Applicant's Japanese Unexamined Utility Model Puplication No. H5-81787, there has been proposed a radio controlled timepiece in which with an antenna formed such that a coil is wound on a core is disposed between a dial plate and a windshield, whereby the antenna is separated from main metal casing that disturbs the radio wave as well as having an unique-designed wristwatch.
Additionally, International Patent Puplication Laid-Open No. WO 95/27928 discloses a wristwatch having a configuration in which an antenna is mounted on a side portion of a casing of the wristwatch.
In addition, European Patent Application Publication No. 0382130 discloses a timepiece in which an antenna is disposed with a form of ring like configuration on the surface of the casing.
However, in the conventional configuration with antenna being disposed over the band, since the antenna is built in the band, it is required to make an electro conduction between the antenna and an electronic device installed inside a main body. As such, sufficient flexibility cannot be imparted to a connection portion between the band and the antenna.
In addition, a metallic band disturbing the radio wave cannot be employed, and thus a connection-dedicated watchband such as a rubber band should be used, consequently arising the problem of material and design limitations.
In the case of the configuration in which the antenna is disposed on an upper surface or a side area thereof, the antenna is separated from the metal portion of the main body of the timepiece. This arises problems in that the timepiece needs to be formed overall to be thick or large, and is therefore subject to design limitations.
In the case of the technique disclosed in European Patent Application Publication No. 0382130, since reception cannot be performed because of the presence of metal in the ring, there arises a problem in that, in practical application, the antenna should be disposed independently of the timepiece.
In addition, Japanese Unexamined Patent Application Publication No. 11-64547 discloses a wristwatch formed such that a coil is provided in a concave portion in a circumferential portion of a circuit board, and a core us disposed in annular arcuate shape extending along the circumferential direction of the circuit board. However, a problem lies in that the manufacturing procedure is complexed, and the operation of assembly in the manufacturing stage is complexed.
In publications such as Japanese Unexamined patent Publication No. 2001-33571 and No. 2001-305244, wristwatches are disclosed in which windshield and bottom cover portions are formed of a non-metallic material such as glass or ceramic material, and a configuration is provided therebetween by using metal materials conventionally used so that radio waves sufficiently reach the antenna.
In summary, according to the conventional examples described above, the configuration thereof was designed based upon the fact that the output of the reception antenna is significantly reduced when it is provided inside the metal outer casing body, and thus in the examples of conventional timepieces, the bottom cover section is formed from the non-metallic material so as to reduce the output reduction and the metal side section is formed from a metal so as to show high level of massive feeling over the timepiece.
Nevertheless, however, in the conventional examples, since the glass or ceramic material is used, the problem arises in that the thickness of the timepiece is increased.
Under these circumstances, conventionally, there exist no way beyond using a high-sensitivity antenna structure with a large size or using the timepiece only in districts in which high radio-wave electric-field intensity is used.
As such, usability required for the radio controlled timepiece is impaired, and the manufacturing cost of the antenna structure, including the design cost is resultantly increased.
In these conventional timepiece having the above-mentioned configurations, it is secured that the radio wave can surely arrive at an antenna of the timepiece, while it gives an impression to a user as if the timepiece is made of metal by applying a thin metallic plating on a bottom cover section thereof.
However, there exists a problem in which each timepiece is in lack of heaviness feeling or massive feeling in its appearance, so that an image for a high quality product is impaired.
In addition, since the reception antenna is built in the metal side section, the output of the antenna is lowered, and hence the reception performance is reduced, accordingly.
Thus, in the past, it was common situation in that a high-quality image radio controlled timepiece having a full metal outer casing body is not yet implemented.
That is, the above-described present inventions are developed in the background in accordance with the following concepts. In the case where the antenna is built in the timepiece, since the bottom cover portion is formed of the metal material, the cover portion has electro-conductivity. As such, even when the radio wave has reached the wristwatch, a magnetic flux is absorbed by the bottom cover portion, whereby the radio wave does not reach the antenna portion.
Accordingly, conventionally, there exist no way beyond using a high-sensitivity antenna structure or using the timepiece only in districts with high radio-wave electric-field intensity. As such, usability required for the radio controlled timepiece is impaired, and the manufacturing cost of the antenna structure, including the design cost is resultantly increased.
Further, in a wristwatch having a configuration in that a bottom cover section is made of the non-metallic material, it is secured that the radio wave can surely arrive at an antenna of the timepiece, while it gives an impression to a user as if the timepiece is made of metal by applying a thin metallic plating on a bottom cover section thereof.
However, there exists a problem in which each timepiece is in lack of heaviness feeling or massive feeling in its appearance, so that an image for a high quality product is impaired.
Further, when the antenna is built in the metal outer casing, a Q value (index of characteristics of the antenna) is reduced, the output (gain) of the antenna is lowered, whereby a problem takes place in that good information communication cannot be implemented.
Thus, conventionally, it is a fact that a radio controlled timepiece with a full metal outer casing offering high quality feeling has not been realized.
Accordingly, an object of the present invention is to solve the conventional problems described above, and to provide an antenna structure usable in a metal outer casing having high reception performance and having neither material limitations nor design limitations, and to provide a radio controlled timepiece using the antenna structure and having a complete metal outer casing.
Another object of the present invention is to provide an antenna device of a wristwatch that prevents the wristwatch from being formed with an increased thickness to be bulky and that offers good wrist wearability.